The present invention relates to an apparatus for forming an enlarged image of a surface to be observed, and more particularly to a surface microscope capable of obtaining the surface topography of an insulator on an atomic scale.
As means for observing the surface of a substance, a scanning tunneling microscope (hereinafter referred to as "STM") has hitherto been known, which can obtain the image of surface atomic arrangement of a substance useful in electric conductivity such as a metal and a semiconductor. However, it is basically impossible to observe an insulator such as ceramics with the STM. As described in an article entitled "Atomic Force Microscope" by G.Binnig et al. (Physical Review Letters, Vol. 56, No. 9, 1986, pages 930 through 933), an atomic force microscope seems to be successful in observing an insulator. However, the structure proposed in the above-referred article does not have the sensitivity sufficient to detect a minute repulsive or attractive force due to an interatomic force.
In the above atomic force microscope, a cantilever is used for detecting the surface irregularities of a sample. It is described in the above article that in an ideal case, the atomic force microscope can measure a force as small as 10.sup.-5 N. In fact, however, an atomic force microscope having a very small cantilever formed of a gold foil cannot detect even a force of 10.sup.-7 to 10.sup.-8 N. In other words, it is impossible to detect the above force with the displacement of the cantilever.